Implemented Caching

[TheodorJ]

Commands that are now cached:

• courses
• asmts

New command options:

• -q/--quiet
  • Doesn't print "Anything missing?" message after subcommand execution
• -i/--ignore-cache
  • Make no reads from or writes to cache in executing this command

Changes to autocompletion:

• Run all autolab-CLI commands in -q mode
• Subcommands of the form 'autolab :' now complete with colon

[TheodorJ]

New command option:

• -u/--use-cache
  • Does not read from server, only prints data in cache